This invention relates to semiconductor integrated circuit devices employing fusible links, such as memories, and more particularly to device structures which also employ a metallic layer which serves to prevent diffusion of a contact metal, such as aluminum, into the semiconductor region where electrical contact is made, such as a shallow emitter region.
Bipolar memory PROMS are turning toward washed emitter processing as the devices become more dense and complex. The present metallization scheme of nichrome fusible links with dual layer aluminum is not compatible with these shallow N+/P junctions due to the interdiffusion of aluminum silicon. Yet, pure aluminum is needed for Schottky diodes. The past approach to solve this problem has been the addition of an aluminum diffusion barrier, such as titanium-tungsten, Ti:W, to the existing metallization scheme. See for example a paper by J. A. Cunningham, C. R. Fuller, and C. T. Haywood, entitled "Corrosion Resistance of Several Integrated Circuit Metallization Schemes", published in IEEE Transactions Rel, Vol. 19, 1970, pp 182-187, and the paper by P. B. Ghate, J. C. Blair, C. R. Fuller and G. E. McGuire, entitled "Application of Titanium-Tungsten Barrier Metallization For Integrated Circuits", published in Thin Solid Films, Vol. 53, 1978, pp 117-128. While this approach should be workable, in practice it presents process problems due to the ready oxidation of both titanium-tungsten and nichrome upon exposure to air, resist processing, acids, as well as making the metallization a more intricate and expensive process.
While there has been some attempt by others to use titanium-tungsten for both fusible link and diffusion barrier purposes, this approach has not proven entirely satisfactory because of the relatively high thickness of titanium-tungsten films required to serve as an effective barrier layer. The resulting thick fuse requires that higher current is needed to fuse satisfactorily. The higher current imposes the need for larger transistors and thicker or wider aluminum interconnects.
A paper by R. R. Nowicki, J. M. Harris, M. A. Nicolet and I. V. Mitchell entitled "Studies of the Ti--W/Au Metallization on Aluminum", published in Thin Solid Films, Vol. 53, 1978, pp 195-205 discloses that nitrided titanium-tungsten is a better diffusion barrier than pure titanium-tungsten when placed between aluminum on silicon and gold. A paper by M. Hill entitled "Magnetron Sputtered Titanium-Tungsten Films", published in Solid State Technology, January 1980, pp 53-59, discloses conventional diffusion barrier structures of titanium-tungsten on silicon followed by aluminum on titanium-tungsten. This paper also discloses the use of oxygen and nitrogen to control the resistivity of titanium-tungsten barrier film.
However, both the paper by Hill and the paper by Nowicki deal solely with the use of titanium-tungsten nitride as a barrier metal layer and there is no suggestion that it would have any special advantages as a fuse material.